This invention relates to soft or semi-hard terpolymers having excellent transparency and low crystallinity, and to a process for preparing same.
As a soft or semi-hard polymer there has heretofore been known polyvinyl chloride. In recent years, moreover, copolymers consisting principally of ethylene have become known. Also, there have been proposed various soft or semi-hard copolymers consisting mainly of propylene, but these copolymers have not yet been put to practical use.
Recently proposed is a process for preparing a soft or semi-hard copolymer by random copolymerization of propylene and 1-butene (see Japanese Patent Laying Open Print No. 79984/1978). This process, however, is not commercially attractive because the expensive 1-butene must be used in large amounts.
Furthermore, in Japanese Patent Laying Open Print No. 104687/1978 there is disclosed a process for preparing a propylene-ethylene copolymer containing 63 to 85 mol% of propylene. However, the copolymer obtained by this process is not satisfactory in strength, it being softer with a Shore A hardness of 30 to 99 and low in tensile strength.
As to terpolymers consisting of ethylene, propylene and .alpha.-olefin of C.sub.4 or more, methods for their preparation are known for example from Japanese Patent Laying Open Prints Nos. 79195/1976 and 26883/1978. In all of these methods, a crystalline terpolymer is prepared using a catalyst comprising the combination of a TiCl.sub.3 -containing component and an organoaluminum compound. These methods, however, are disadvantageous in that a soft or semi-hard copolymer cannot be obtained.
It is an object of this invention to provide soft or semi-hard terpolymers having excellent transparency and low crystallinity, and a process for preparing same.
Other objects and advantages of this invention will become apparent from the following description.